This invention relates to quarter-turn valves, such as butterfly valves, ball valves, plug cocks and the like and, more particularly, to quarter-turn valves including a supervisory switch assembly.
In some fluid operations, it is essential that certain control valves are maintained either in the fully open position or in the fully closed position during normal operation. For example, in fire protection sprinkler systems, the control valves must be fully open at all times in order to insure proper water flow in the event of an emergency. When a centralized monitoring system is used, a so-called supervisory switch is installed on the critical control valves. This switch is connected into an electrical system which produces a warning signal to energize an alarm, turn on a light, or the like in the event an unauthorized person starts to open or close one of the control valves.
Such supervisory switches typically are not manufactured by the valve manufacturer, are installed in the field and, thus, are not an integral part of the valve. Most prior supervisory switches are quite complex, making them quite costly and requiring special skills for installation and maintenance. Also, prior supervisory switches tend to be bulky and protrude some distance from the valve, making them vulnerable to being accidentally bumped or struck by equipment and damaged, knocked out of adjustment, or otherwise rendered inoperable.
Some prior supervisory switches include means for triggering a signal in the event someone tampers with the switch housing. However, such trigger means usually are relatively complex and/or require additional parts which add to fabrication and maintenance costs, as well as increased unreliability.